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24 
25 #ifndef SHARE_RUNTIME_TASK_HPP
26 #define SHARE_RUNTIME_TASK_HPP
27 
28 #include "memory/allocation.hpp"
29 #include "runtime/timer.hpp"
30 
31 // A PeriodicTask has the sole purpose of executing its task
32 // function with regular intervals.
33 // Usage:
34 //   PeriodicTask pf(10);
35 //   pf.enroll();
36 //   ...
37 //   pf.disenroll();
38 
39 class PeriodicTask: public CHeapObj<mtInternal> {
40  public:
41   // Useful constants.
42   // The interval constants are used to ensure the declared interval
43   // is appropriate;  it must be between min_interval and max_interval,
44   // and have a granularity of interval_gran (all in millis).
45   enum { max_tasks     = 10,       // Max number of periodic tasks in system
46          interval_gran = 10,
47          min_interval  = 10,
48          max_interval  = 10000 };
49 
num_tasks()50   static int num_tasks()   { return _num_tasks; }
51 
52  private:
53   int _counter;
54   const int _interval;
55 
56   static int _num_tasks;
57   static PeriodicTask* _tasks[PeriodicTask::max_tasks];
58   // Can only be called by the WatcherThread
59   static void real_time_tick(int delay_time);
60 
61   // Only the WatcherThread can cause us to execute PeriodicTasks
62   friend class WatcherThread;
63  public:
64   PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
65   ~PeriodicTask();
66 
67   // Make the task active
68   // For dynamic enrollment at the time T, the task will execute somewhere
69   // between T and T + interval_time.
70   void enroll();
71 
72   // Make the task deactive
73   void disenroll();
74 
execute_if_pending(int delay_time)75   void execute_if_pending(int delay_time) {
76     // make sure we don't overflow
77     jlong tmp = (jlong) _counter + (jlong) delay_time;
78 
79     if (tmp >= (jlong) _interval) {
80       _counter = 0;
81       task();
82     } else {
83       _counter += delay_time;
84     }
85   }
86 
87   // Returns how long (time in milliseconds) before the next time we should
88   // execute this task.
time_to_next_interval() const89   int time_to_next_interval() const {
90     assert(_interval > _counter,  "task counter greater than interval?");
91     return _interval - _counter;
92   }
93 
94   // Calculate when the next periodic task will fire.
95   // Called by the WatcherThread's run method.
96   // Requires the PeriodicTask_lock.
97   static int time_to_wait();
98 
99   // The task to perform at each period
100   virtual void task() = 0;
101 };
102 
103 #endif // SHARE_RUNTIME_TASK_HPP
104